The glass dewar does not have a protective coating, and is under vacuum. Be very careful, use behind shield

Chemicals and Solutions:

Materials:

To show reactivity:

clear plastic safety shield

clear glass dewar of liquid oxygen

cigarette without filter

matches

tweezers

gloves and goggles

To show paramagnetism of oxygen:

clear glass dewar of liquid oxygen

test tube

Very large Alnico magnet.

Telescoping T-support stand.

About 4 feet of string to support tube of oxygen.

gloves and goggles

Procedure:

Liquid oxygen is not available in the building. Advance notice must be given to allow time to prepare.*

Obtain at least 4 liters of liquid nitrogen. Use the oxygen setup located in the hood of Room 191A to prepare the liquid oxygen. Basically, oxygen is blown into a flask that is being cooled in a dewar of liquid nitrogen (the boiling point of nitrogen is -196oC, whereas liquid oxygen has a boiling point of -182oC).

A few pointers:

Be sure to rinse the pear shape flask with a little liquid N2 before starting.

Keep a slight negative pressure on the oxygen line.

Cool the clear dewar with liquid nitrogen before transferring the liquid oxygen from the flask.

When transferring the liquid oxygen to the clear dewar pour it through glass wool to catch any ice crystals.

Holding the filterless cigarette with tweezers, first soak it in liquid oxygen and then ignite it.

To show paramagnetism, hang a test tube from a T-bar ringstand with string. Pour liquid oxygen into the test tube. If a strong magnet is brought near, the tube of liquid oxygen will begin to sway. Paramagnetic substances are attracted to a magnetic field. Paramagnetism is a property shown by substances containing unpaired electrons. The outer ten electrons of O2 fill the following molecular orbitals: 2s, *2s, 2p, 2p, *2p. The final two electrons of O2 enter into the two equal *2p orbitals singly. They are unpaired and therefore oxygen is paramagnetic. (Diamagnetic substances, like nitrogen, are repelled by a magnet. They do not have unpaired electrons.)

Hint:

Discussion:

The transition responsible for the pale blue color of liquid oxygen is the simultaneous excitation of two molecules from triplet sigma to singlet delta. The double excitation avoids the spin forbiddeness. The energy for the transition corresponds to a wavlenght of 650 nm. Absorbing in the red means the liquid oxygen looks blue. This is only possible in the high density of the liquid so air doesn/t have this absorption with any intensity.